Condensation, Damp and Mould

This page has advice about how to identify and reduce condensation, and how to treat the mould growth that often comes with it. 

Damp can cause mould on walls and furniture and make window frames rot. Damp housing encourages the growth of mould and mites. Mites feed on mould and can increase the risk of respiratory illnesses in some people.

There are four main types of damp that could affect your home. The one you need to watch out for the most is condensation.


Condensation is the biggest cause of damp in the home. It is caused when water vapour or moisture from inside comes into contact with a colder surface, like a window or wall. The resulting water drops (condensation) can then soak into your wallpaper, paintwork or even plasterwork. In time, these damp areas can attract black mould. 

Condensation mainly occurs during the colder months, and can happen whether it is rainy or dry. It is usually found in the corners of rooms, north facing walls and on or near windows. It is also found in areas where there is poor air circulation, such as behind wardrobes and beds, especially if they are pushed up against external walls.

Black mould is frequently seen with this type of dampness.

Condensation and Mould Growth

Most homes are affected by condensation at some point, but certain activities can increase the problem. Condensation and mould growth is often due to lifestyle. It is something that you can reduced or remedy without expensive work or treatment. 

Cooking, washing, drying clothes indoors, even breathing - all produce water vapour that can only be seen when tiny drops of water (condensation) appear on colder surfaces such as walls, windows, ceilings or mirrors. 

The amount of condensation in a home depends on three things: 

  • how much water vapour is produced by the actions of the residents
  • how cold or warm the property is
  • how much air circulation (ventilation) there is

Simply turning up the heating will not sort out the problem. You need to look at all of the three factors to reduce the problem.

The first sign of a problem is water vapour condensing on windows and other cold surfaces, and which takes a long time to disappear. This then allows surfaces to become damp.

The second indication is black mould patches growing on these damp areas. 

Mould needs four things to thrive:

  • moisture
  • food - such as wallpaper or emulsion paint
  • the right temperature
  • oxygen

If you deal with these issues, you will automatically deal with the mould. 

Common Household Moisture Producing Activities

Our everyday activities add extra moisture to the air inside our homes. Even our breathing adds some moisture. One person sleeping adds half a pint of water to the air overnight and an active person adds twice that rate during the day. This list shows how much extra water you could be adding to the air in your home in a day:

  • 2 people at home (16 hours) - 3 pints
  • a bath or shower - 2 pints
  • drying clothes indoors - 9 pints
  • cooking and use of a kettle - 6 pints
  • washing dishes - 2 pints
  • bottled gas heater (8 hours use) - 4 pints

Warmth versus Ventilation

You need to get the balance right between warmth and ventilation as this is important and can be very effective.

You may think that you are losing heat by opening windows or ventilating your home, but what you are actually doing is allowing warm moist air to escape and letting cool dry air enter. It is cheaper to heat dry cool air than it is to heat warm moist air! So if you have trickle vents, use them. Or open your windows slightly for a short period of time - between 30 minutes and one hour. Don't leave your windows open all day.

Six Steps to Reducing Condensation and Mould Growth

1. Produce Less Moisture

Ordinary daily activities produce a lot of moisture.To reduce this:

  • dry clothes outdoors if possible. Avoid drying clothes indoors or if you have to, dry them on a clothes airer in the bathroom with the door closed and either an extractor fan on or a window slightly open. Vent tumble driers to the outside (never into the home) or buy a condensing type
  • Cover pans when cooking and do not leave kettles boiling
  • Do not use paraffin or gas bottle heaters. They produce large amounts of water vapour and are very expensive to run

2. Remove Excess Moisture 

Always wipe the windows and window sills of your home every morning to remove condensation. This is especially important in the bedroom, bathroom and kitchen - just opening the window is not enough. 

3. Heating

When it's cold, the best way to keep rooms warm and avoid condensation is to keep a low background heat on all day rather than short bursts of high heat when you are in the house. Good heating controls on your radiators, an independent room thermostat and a timer will help you control the heating throughout your house and help manage heating costs. Also think about better insulation (roof, cavity –wall or external wall insulation), draught-proofing windows and doors, and installing double or secondary glazing.

4. Ventilation

It is important to remove condensation and excess moisture by ventilating rooms. You can ventilate a room without making it draughty or cold. Just open the window slightly or use the trickle vent that's often on new windows. This allows warm, moist air to escape outside and lets cool dry air into the property. 

Here are some tips to help with ventilation: 

  • Always ventilate or open a window when using the kitchen or the bathroom and close the doors to prevent moisture in the air from spreading to other parts of the house. Continue to ventilate these rooms for a short time after a shower, bath or cooking and keep the door closed
  • Open bedroom windows for up to one hour as soon as you get up 
  • Clear window sills of clutter that will restrict opening the window and prevent surfaces from being wiped
  • Leave space between the back of furniture and cold walls for air to circulate
  • Ventilate cupboards and wardrobes, and avoid overfilling them as this prevents air circulating
  • Do not completely block chimneys and flues – fit with an air vent and make sure you meet ventilation requirements for any gas appliances in a room. 

5. Insulation

Insulating and draught-proofing will help keep your home warm and save money on your heating bills. 

  • Insulate the loft to a depth of 300mm
  • Consider secondary or double glazing
  • Consider cavity wall insulation or internal dry lining
  • Draught-proof windows and external doors. When draught-proofing, do not block permanent ventilators or rooms requiring ventilation
  • Find out if you are eligible for a grant for insulating your home, this may help to reduce your bills.

6. Dealing with Mould

Mould can grow on walls, ceilings, furnishings and even on clothes and toys, which can be depressing and expensive. To kill and remove the mould: 

  • Carefully remove excess mould with a damp cloth and throw away afterwards. Or if possible use a vacuum cleaner and empty afterwards. Do not brush mould as this releases spores into the air
  • Wipe down affected areas using a fungicidal wash or diluted bleach – remember always use rubber gloves and wear safety glasses
  • After treatment redecorate using a fungicidal paint – do not paint over using an ordinary paint as mould is likely to grow back
  • Dry clean affected clothes and shampoo carpets where necessary
  • Regularly check under divan bed drawers, behind wardrobes, bedside cabinets, bedheads and clothing stored in cupboards, and wipde down any affected areas

Dealing with condensation and mould growth is not easy. Just doing one or two of the six steps may not solve your problem - you need to do as much as possible every day. Once a balance has been achieved your situation should improve over time. 

Landlord responsibilities

Landlords should:

  • work with tenants to determine the cause of the problem
  • carry out repairs to make good any defects identified at the property
  • arrange for redecoration after any treatment and use specialist bathroom or kitchen paint, or wallpaper paste with an anti-fungicidal additive 
  • avoid using wallpaper in bathrooms and kitchens
  • provide mechanical ventilation with a humidity sensor

Other types of damp

Penetrating Dampness 

This type of dampness is usually found on external walls or due to roof leaks on ceilings. It only appears because of a defect outside the home, such as missing pointing, cracked rendering, missing roof tiles or defective guttering and pipes. These defects allow water to pass from the outside to the inner surfaces. Penetrating dampness is far more noticeable following rainfall and will normally appear as a well defined damp-patch which looks and feels damp to the touch.

Black mould is rarely seen on areas of penetrating damp. The affected areas are usually too wet and the dampness contains salts picked up when passing through the wall, which prevent the growth of black mould.

Defective Plumbing

Leaks from water and waste pipes, especially in bathrooms and kitchens, are relatively common. Affected areas look and feel damp to the touch and remain damp whatever the weather conditions outside. You will usually find the source of the problem if you look for issues around:

  • the water and waste pipes that serve the kitchen and bathroom
  • the seals around the bath, shower and sinks
  • the external pipework, such as guttering will usually find the source of the problem. 

Black mould is rarely seen with this type of dampness. The area is usually too wet and the chemicals in a waste waterleak will will prevent mould growth. 

Rising Damp

This is generally caused by water rising from the ground into the home. The water gets through or round a broken damp proof course (DPC) or passes through the natural brickwork if the property has no DPC. Rising damp usually only affects basements and ground floor rooms. It normally rises 12 to 24 inches above ground level and usually leaves a tide mark low on the wall. You may also notice white salt marks on the affected areas. These are called efflorescence salts. 

Rising damp will be present all year round, but is more noticeable in winter. If lit's not treated, it can cause wall plaster to crumble and wallpaper to lift. 

Black mould is not usually seen where there is rising damp. This is because rising dampness carries with it ground salts which prevent the growth of black mould.